Republican Jeb Bush will visit three U.S. allies, Germany, Poland and Estonia, in early June to get a first-hand view of European economic and security challenges as he explores a run for his party's presidential nomination in 2016, a Bush aide said on Monday.

Foreign policy has been growing in importance in the battle to determine President Barack Obama's successor, with Republicans questioning Obama's handling of the threat from Islamic State and Russia's aggression against Ukraine.

Bush's visit will give him a chance to lay out his differences with Obama, a Democrat, particularly when it comes to NATO as alliance members Poland and Estonia watch events in Ukraine with alarm. Polish politicians have repeatedly called for increased U.S. military presence in the region.

The U.S. presidential election will be held in November 2016.

Bush told talk radio host Hugh Hewitt on March 30 that Russian President Vladimir Putin is a "ruthless pragmatist" and the United States should let Moscow know of U.S. determination to protect the alliance and its members.

His visit will also allow him to distinguish his foreign policy views from those of Hillary Clinton, the overwhelming favorite for the Democratic presidential nomination.

In Germany, the former Florida governor will address the governing Christian Democratic Union economic conference, said Bush's aide, who requested anonymity.

In Poland and Estonia, Bush will meet government and business leaders and leaders of civic and other organizations.

Bush spokeswoman Kristy Campbell said that in all three countries Bush will discuss policies to promote growth, innovation and technologies to address the changing global economic environment and ways to foster prosperity on both sides of the Atlantic.

"He will also be listening to their perspectives on growing security challenges in the region," she said.

Announcement in June?

An aide said the 62-year-old Bush, who is the brother of former President George W. Bush, has yet to decide whether to run for president. Other sources close to Bush's camp have said his team has discussed the possibility of an announcement in June, after the trip.

David Yepsen, director of the Paul Simon Public Policy Institute at Southern Illinois University, said Bush's trip is significant because foreign policy and military affairs are playing a more important role in the 2016 campaign than they did in 2008 and 2012.

But, he said, Bush should be cautious because it is easy to make mistakes on a global stage.

"It can backfire on you," he said.

In recent months two rivals, Wisconsin Governor Scott Walker and New Jersey Governor Chris Christie, travelled to Europe, where Walker stumbled on the subject of evolution and Christie drew criticism for offering no insight into how he would conduct foreign policy.

In 2012, then Republican nominee Mitt Romney visited London, Jerusalem and Poland in a trip that was noteworthy for a number of gaffes.

Bush would be in the top tier of contenders for the Republican nomination if he decided to run, but he has been unable to break away from a host of rivals in national polls of Republicans. A CNN/ORC opinion poll released on Monday showed him leading the pack with 17 percent support, and Walker in second place with 12 percent.

Republican U.S. Senator Marco Rubio of Florida, who announced a week ago that he was running for the White House, has made foreign policy a hallmark of his candidacy based on his being a member of the Senate Foreign Relations Committee.

Bush has offered a hawkish view of Obama's foreign policy.

He has questioned concessions Obama might make to secure a nuclear deal with Iran, criticized his diplomatic opening to Cuba, and called Obama "feckless" for not providing defensive equipment sought by Ukraine.

Bush has been on 89 foreign trips to 29 countries and six continents since he left the governor's office in Florida in 2007. His last trip to Germany was in 2011. This will be his first trip to Poland and Estonia, the Bush team said.